Brain MRI in a 6-year-old girl with a history of congenital HIV and toxoplasmosis infection revealed polymicrogyria and white matter findings suggestive of congenital CMV infection. In addition, a smaller right trigeminal nerve (Fig. 1 curved arrow), a cleft extending into the smaller right cerebellar hemisphere (Fig. 1 straight arrow) and fatty infiltration of the right temporalis muscle (Figs. 1 and 2 arrowheads) were seen. The gyral pattern in the right inferior temporal lobe was abnormal. The striking fatty infiltration of the muscles of mastication was likely a result of right trigeminal nerve hypoplasia caused by a vascular or infective insult to the brainstem [1]. These findings were present in retrospect on studies obtained in the postnatal period, but less conspicuous due to the smaller size of the patient.

Fig. 1
figure 1

Axial T2-W image at the level of the trigeminal nerve

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Fig. 2
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Coronal MPRAGE image

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